# std::bad_function_call

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
class bad_function_call; |  |

`std::bad_function_call` is the type of the exception thrown by `std::function::operator()` if the function wrapper has no target.

Inheritance diagram

### Member functions

(constructor) | constructs a new `bad_function_call` object (public member function)
operator= | replaces the `bad_function_call` object (public member function)
what | returns the explanatory string (public member function)

## std::bad_function_call::bad_function_call

bad_function_call() noexcept; | (1) | (since C++11)
bad_function_call( const bad_function_call& other ) noexcept; | (2) | (since C++11)

Constructs a new `bad_function_call` object with an implementation-defined null-terminated byte string which is accessible through `what()`.

1) Default constructor.
2) Copy constructor. If *this and other both have dynamic type `std::bad_function_call` then std::strcmp(what(), other.what()) == 0.

### Parameters

other | - | another exception object to copy

## std::bad_function_call::operator=

bad_function_call& operator=( const bad_function_call& other ) noexcept; |  | (since C++11)

Assigns the contents with those of other.If *this and other both have dynamic type `std::bad_function_call` then std::strcmp(what(), other.what()) == 0 after assignment.

### Parameters

other | - | another exception object to assign with

### Return value

*this

## std::bad_function_call::what

virtual const char* what() const noexcept; |  | (since C++11)

Returns the explanatory string.

### Return value

Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a std::wstring. The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.

The returned string is encoded with the ordinary literal encoding during constant evaluation. | (since C++26)

### Notes

Implementations are allowed but not required to override `what()`.

## Inherited from std::exception

### Member functions

(destructor) [virtual] | destroys the exception object (virtual public member function of `std::exception`)
what [virtual] | returns an explanatory string (virtual public member function of `std::exception`)

### Example

Run this code

    #include <functional>
    #include <iostream>

    int main()
    {
        std::function<int()> f = nullptr;
        try
        {
            f();
        }
        catch (const std::bad_function_call& e)
        {
            std::cout << e.what() << '\n';
        }
    }

Possible output:

    bad function call

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2233 | C++11 | `what()` always returned the same explanatory string as `std::exception::what()` | returns its own explanatory string

### See also

function (C++11) | copyable wrapper of any copy constructible callable object (class template)

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